Conventionally, multilayer films of polyolefin resins such as polypropylenes and polyethylenes are widely used for formation of drug containers such as infusion solution bags. In recent years, multi-chamber containers in which a plurality of drugs can be separately contained and mixed with each other for use are widely employed in the field of medical containers.
For such a multi-chamber container, it is important to properly control the unsealability of a weakly sealed portion which isolates adjacent container portions from each other. In order to stably store a drug in the multi-chamber container, it is necessary to form the multi-chamber container from a film having an excellent gas barrier property. It is also important to take into consideration the unsealability as well as the transparency, the mechanical strength, the sterilization heat resistance, the antiblocking property and other properties of a multilayer film for the multi-chamber container, and the prevention of exudation of additives from the multilayer film into the inside of the container (contamination resistance). Therefore, the layered structure of the multilayer film is designed so as to properly control these properties.
Patent Document 1 discloses a five-layer film including a first layer (outermost layer) and a fifth layer (innermost layer) each composed of a linear ethylene/α-olefin copolymer having a density of 0.930 to 0.950 g/cm3, a second layer and a fourth layer each composed of a resin mixture containing a linear very-low-density ethylene/α-olefin copolymer prepared by employing a metallocene catalyst and having a density of 0.860 to 0.920 g/cm3 and a high-density polyethylene having a density of 0.955 to 0.970 g/cm3, and a third layer composed of a cycloolefin copolymer. Patent Document 1 also discloses a container formed of the five-layer film.
Patent Document 2 discloses a medical container formed of a film including a resin composition layer (A) composed of a resin composition containing a thermoplastic norbornene polymer and a polyethylene, coating layers (B) bonded to opposite surfaces of the resin composition layer (A) and each composed of a composition containing an ethylene/α-olefin copolymer having a density of 880 to 930 kg/m3 with the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) being 1.5 to 4.0, and polyethylene layers (C) each composed of a high-density polyethylene and respectively bonded to the coating layers (B).
Patent Document 3 discloses a four-layer film including a surface layer composed of an ethylene/α-olefin copolymer having a density of 0.935 to 0.950 g/cm3 and having a thickness of 10 to 50 μm, a flexible layer composed of an ethylene/α-olefin copolymer having a density of 0.860 to 0.930 g/cm3 and having a thickness of 100 to 200 μm, a barrier layer composed of a resin mixture containing 60 to 95% by weight of a polycycloolefin and 5 to 40% by weight of an ethylene/α-olefin copolymer having a density of 0.900 to 0.965 g/cm3 and having a thickness of 10 to 80 μm, and a seal layer composed of an ethylene/α-olefin copolymer having a density of 0.910 to 0.950 g/cm3 and having a thickness of 5 to 80 μm. Patent Document 3 also discloses a container formed of the four-layer film.
Patent Document 4 discloses a flexible plastic film including a seal layer composed of a mixture containing a propylene/α-olefin random copolymer and a polypropylene homopolymer, a first flexible layer provided on a surface of the seal layer and composed of a mixture of a propylene/α-olefin random copolymer or the like and an ethylene/α-olefin copolymer elastomer, a reinforcement layer provided on a surface of the first flexible layer and composed of a polycycloolefin or the like, a second flexible layer provided on a surface of the reinforcement layer and composed of a mixture of a propylene/α-olefin copolymer elastomer or the like and an ethylene/α-olefin copolymer elastomer, and an outermost layer provided on a surface of the second flexible layer and composed of a propylene/α-olefin random copolymer or the like. Patent Document 4 also discloses a container formed of the flexible plastic film.    Patent Document 1: JP-A-2002-301796    Patent Document 2: JP-A-2004-121824    Patent Document 3: JP-T-2005-525952    Patent Document 4: JP-A-2006-21504